The present invention relates to a device for anchoring a probe lowered into a wall, by opening mobile arms, which come to bear against the well thereof.
More particularly, the invention relates to a device for anchoring, by opening mobile arms, a probe equipped with measuring means lowered into a well for studying the geological formations encountered or for carrying out seismic prospection operations, probe being fixed at the end of a multifunction cable containing electric wires and signal transmission lines between the measuring apparatus and a surface installation.
In, for example, French Patent Application No. 2,501,380, a system for anchoring devices lowered at the end of a cable into holes or wells drilled in the ground is proposed which includes at least one one pivoting arm associated with drive means, which drive means may comprise for example, hydraulic jacks for actuating the arms. The hydraulic jacks communicate through a hydraulic circuit, with a cylinder in which a piston is sealingly drives by, for example, an electric motor.
The drive means may, as proposed in French Pat. Nos. 2,052,062 and 2,138,335, also be formed by springs adapted, by extending, to move the anchorage arms apart, the extension movement of the springs being opposed by mechanical elements movable under the action of a hydraulic system contained in the body of the probe and actuated from the surface installation.
In accordance with the present invention, an anchorage device comprises at least one spring, a rod driven in translation by the expansion of the spring, means for transforming the translational movement of the rod into a pivoting movement of the anchorage arms and means for intermittently immobilizing the rod in the compression position of the spring, with the the immobilization means comprising a bolt adapted to a radial recess in the rod in the compression position of the spring, and hydraulic means for moving the bolt.
The hydraulic means may comprise a cavity formed in the body of the apparatus, a head firmly secured to the bolt in translation and adapted to slide in the cavity, and a hydraulic circuit for intermittently applying unequal pressures to the two opposite faces of the head, with one of the pressures being equal to the pressure existing in the well at the chosen depth where the apparatus is immobilized. The application of the two unequal pressures is effected by, for example, an electromagnetic valve.
Since the device is most frequently used at a depth of several hundred meters where the pressure is very high, the force to which the bolt is subjected, due to the differential pressure applied to the piston, is considerable and provides a very reliable and very clean tripping of the opening of the arm.
Moreover, this high tripping force is obtained without using an independent pressurized fluid generator driven by an electric motor requiring a considerable electrical power supply.
Since the control system is formed essentially by an electromagnetic valve, the electric power supply of the probe is simplified.
It should also be emphasised that the force for opening the arm, which is linked to an overpressure occurring solely during lowering of the apparatus into the well, is zero at the surface and that accidental arm tripping after compression of the spring and locking is impossible as long as the apparatus is not in its normal conditions of use.